I kind of misspoke about the fronts. Just that there are no pre-molded flares. Plenty of universal ones, mostly made of rubber, that can be fitted to the opening to widen it a bit.
Better to keep the wheels tucked in as much as possible I think. But even that might not be enough in itself to keep the spray off the windshield completely.
I don't think the rubber ones I've seen are easily fitted to the sheet metal the way a Bronco's is formed. And I also don't think they look very complementary. Either to the way the rears are with flares, or even just to the body itself. But that's a personal "style" opinion rather than a functional one.
I've just never had that issue with spray, but I also live where it's mostly dry most of the time.
For durability, the fiberglass flares are actually quite robust. As long as they're not impacted by something, they rarely fail even with age. The worst that can be said is that they crack a little around the rivets. But the weaker plastic ones did that even sooner than glass did. The later generations of plastic (usually ABS) don't stress crack near as much as they did in the seventies to early eighties, but "might" still have that issue with extended use. Not sure yet.
Most of our modern plastic flares are designed to create as big of an opening for tires as possible. But Bushwacker still makes their original size, which mimics the old glass flares pretty good. In fact, when I first replaced my original fiberglass rear flares (installed by the original owner or selling dealer in '71) in the early nineties, the Bushwackers not only fit the same opening, but all the holes lined up almost perfectly.
Still available, we sell them as our part #5625. Black only of course, but made of their newest Duraflex (ABS base) and still to the original profile.
With so many brands of fiberglass out there thirty years ago, it's hard to guarantee that the current Bushwacker will fit yours as good as it did mine, but at least it's a better chance than anything else on the market. Even some fiberglass ones I would imagine.
Good luck. Either way you go though, I don't think you could go wrong with either glass or plastic. If you intend to off-road much (or bounce around parking lots looking for shopping carts to bash?) go with plastic. If you don't see your truck being hit with any tree branches, cattle fences, or rocks anytime soon, and prefer white without having to paint, fiberglass should be just fine.
Paul